New Horizons encountered Ultima 6.5 billion km from Earth.
Around 10 hours after reaching the icy world of Ultima Thule, in the early part of New Year's Day, the New Horizons vessel got in touch with scientists back home. The New Horizons team has named the individual lobes, calling the smaller one Thule and the larger one Ultima. It was the fastest spacecraft ever launched at the time (only recently supplanted by NASA's Parker solar mission), and the fifth manmade object to reach solar escape velocity.
Scientists are keen to study Ultima Thule as it lives in a region that has been relatively untouched since the formation of the solar system, which in turn helps them better understand planetary formation. Kuiper belt objects "are the first planetesimals", he said. This image was taken by the craft's Multispectral Visible Imaging Camera (MVIC), which combines light from the infrared, red and blue channels. The lobes, he said, were really only "resting on each other". Is it two icy objects orbiting each other, or a single "peanut"?
About the size of a city, Ultima Thule has a mottled appearance and is the color of tiresome brick, probably because of the effects of radiation bombarding the icy surface, with brighter and darker regions. Scientists say no impact craters could be seen in the latest photos.
We have a lot more data to download from New Horizons over the coming months at the painfully slow rate of one kilobit per second. "New Horizons has set a new bar for state-of-the-art spacecraft navigation".
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With the obvious warning that with only 1% of the data in-hand that some of this will change, here's what we now know about 2014 MU69 based on those initial science returns.
It also looks pristine, nearly unchanged since it formed out of a disk of dust and gas that orbited the sun more than 4.5 billion years ago. That's right, as New Horizons passed this object, NASA had beamed radar pulses at it, to bounce off at just the right moment, so that New Horizons would pick up the radar reflections. Then the spheres slowly spiralled closer to each other and stuck together. Closer to the sun, these building blocks would go on to form Earth, Mars, and all the other planets.
"It's a time machine to time zero", said Jeff Moore, the mission's geophysics lead investigator from NASA Ames.
Scientists weren't able to confirm the flyby until several hours later.
It showed Ultima Thule, formally known as 2014 MU69, is actually a pair of reddish spheres that have been fused together by gravity, they said.
NASA Administrator Jim Bridenstine congratulated NASA's New Horizons team, Johns Hopkins Applied Physics Laboratory and the Southwest Research Institute for "making history".